package main

import (
	"errors"
	"io/fs"
	"mime"
	"net"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

const (
	publicClientLimit = 30
	publicGlobalLimit = 300
)

var publicDownloadNames = map[string]struct{}{
	"SHA256SUMS":                    {},
	"lrc-local-windows-amd64.exe":   {},
	"lrc-local-linux-amd64.tar.gz":  {},
	"lrc-local-darwin-arm64.tar.gz": {},
	"lrc-local-darwin-amd64.tar.gz": {},
}

type rateWindow struct {
	started time.Time
	seen    time.Time
	count   int
}

type publicApp struct {
	origin      string
	host        string
	downloadDir string
	web         fs.FS
	core        *localApp
	sem         chan struct{}
	mu          sync.Mutex
	global      rateWindow
	clients     map[string]rateWindow
}

func newPublicApp(origin, downloadDir string, web fs.FS, qq qqAPI) (*publicApp, error) {
	parsed, err := url.Parse(origin)
	if err != nil || parsed.Scheme != "https" || parsed.Host == "" || parsed.Path != "" {
		return nil, errors.New("public origin must be an HTTPS origin without a path")
	}
	now := time.Now()
	return &publicApp{
		origin: origin, host: parsed.Host, downloadDir: downloadDir, web: web,
		core: newApp(origin, "", web, qq), sem: make(chan struct{}, 12),
		global: rateWindow{started: now, seen: now}, clients: make(map[string]rateWindow),
	}, nil
}

func (a *publicApp) routes() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /", a.index)
	mux.HandleFunc("GET /app.js", a.asset("app.js", "text/javascript; charset=utf-8"))
	mux.HandleFunc("GET /styles.css", a.asset("styles.css", "text/css; charset=utf-8"))
	mux.HandleFunc("GET /api/info", func(w http.ResponseWriter, _ *http.Request) {
		writeJSON(w, http.StatusOK, map[string]any{"mode": "public", "version": version})
	})
	mux.HandleFunc("POST /api/search", a.withAPI(a.core.search))
	mux.HandleFunc("POST /api/lyrics", a.withAPI(a.core.lyrics))
	mux.HandleFunc("GET /download/{name}", a.download)
	mux.HandleFunc("GET /health", func(w http.ResponseWriter, _ *http.Request) {
		writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
	})
	return a.securityHeaders(mux)
}

func (a *publicApp) securityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "no-store")
		w.Header().Set("Cross-Origin-Opener-Policy", "same-origin")
		w.Header().Set("X-Frame-Options", "DENY")
		next.ServeHTTP(w, r)
	})
}

func (a *publicApp) index(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		http.NotFound(w, r)
		return
	}
	a.serveFile(w, r, "app.html", "text/html; charset=utf-8")
}

func (a *publicApp) asset(name, contentType string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) { a.serveFile(w, r, name, contentType) }
}

func (a *publicApp) serveFile(w http.ResponseWriter, r *http.Request, name, contentType string) {
	data, err := fs.ReadFile(a.web, name)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Type", contentType)
	_, _ = w.Write(data)
}

func (a *publicApp) download(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("name")
	if _, allowed := publicDownloadNames[name]; !allowed || a.downloadDir == "" {
		http.NotFound(w, r)
		return
	}
	path := filepath.Join(a.downloadDir, name)
	file, err := os.Open(path)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil || !info.Mode().IsRegular() {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Disposition", `attachment; filename="`+name+`"`)
	http.ServeContent(w, r, name, info.ModTime(), file)
}

func (a *publicApp) withAPI(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		mediaType, _, _ := mime.ParseMediaType(r.Header.Get("Content-Type"))
		if r.Header.Get("Origin") != a.origin || mediaType != "application/json" {
			writeJSON(w, http.StatusForbidden, map[string]string{"error": "请求来源无效"})
			return
		}
		if !a.allowRequest(clientAddress(r)) {
			w.Header().Set("Retry-After", "60")
			writeJSON(w, http.StatusTooManyRequests, map[string]string{"error": "请求过于频繁，请稍后再试"})
			return
		}
		select {
		case a.sem <- struct{}{}:
			defer func() { <-a.sem }()
		case <-time.After(time.Second):
			writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "当前请求较多，请稍后重试"})
			return
		}
		r.Body = http.MaxBytesReader(w, r.Body, 16*1024)
		next(w, r)
	}
}

func clientAddress(r *http.Request) string {
	if forwarded := net.ParseIP(strings.TrimSpace(r.Header.Get("X-Real-IP"))); forwarded != nil {
		return forwarded.String()
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err == nil {
		return host
	}
	return "unknown"
}

func (a *publicApp) allowRequest(client string) bool {
	a.mu.Lock()
	defer a.mu.Unlock()
	now := time.Now()
	if now.Sub(a.global.started) >= time.Minute {
		a.global = rateWindow{started: now, seen: now}
	}
	if a.global.count >= publicGlobalLimit {
		return false
	}
	entry := a.clients[client]
	if entry.started.IsZero() || now.Sub(entry.started) >= time.Minute {
		entry = rateWindow{started: now, seen: now}
	}
	if entry.count >= publicClientLimit {
		return false
	}
	entry.count++
	entry.seen = now
	a.clients[client] = entry
	a.global.count++
	a.global.seen = now
	if len(a.clients) > 2048 {
		for address, candidate := range a.clients {
			if now.Sub(candidate.seen) > 10*time.Minute {
				delete(a.clients, address)
			}
		}
	}
	return true
}